Spray coating apparatuses which apply flammable liquid coating materials onto work parts are old and well known in the art. With the evolution of industrial safety standards, however, precautions must now be taken to prevent the accidental explosion or ignition of the flammable coating material sprayed during the coating operation. For this purpose, the work part is enclosed within a spray booth during the coating operation. Much care is taken to eliminate electrical components from the interior of the spray booth due to the possibility of an electric spark resulting from shorting wires, etc. inside the spray booth. It has been the practice, therefore, to actuate valves and the like with pneumatic signals instead of electrical signals due to the inability of pressurized air to create a spark.
Typically, in industrial spray coating operations, e.g., the mass quantity painting of motor vehicle bodies, a different color of paint may be required for each work part to be coated. A manifold-like color changer is provided to supply numerous colors of coating materials to the discharge atomizer. As described above, pneumatic valves, i.e., needle valves, are associated with the color changer for supplying a particular color of paint to the discharge atomizer at a predetermined time in response to a pneumatic signal. The pneumatic signal is sent from an automatic timing means, e.g., a computer controlled solenoid valve associated with a supply of compressed air, from outside the spray booth. The pneumatic signal, traveling through a feed hose extending into the spray booth to the pneumatic valve, actuates the valve to allow a particular color of paint to flow to the discharge atomizer.
The prior art spray coating apparatuses as described above are deficient in several respects. First, the prior art systems are inherently sluggish. That is, the response time between the sending of the pneumatic signal from outside the spray booth to the actuation of the pneumatic needle valve can be as much as several seconds. This is because a relatively large distance is traversed between the means for sending the pneumatic signal outside of the spray booth to the pneumatic valve inside of the spray booth. This requires that each spray coating apparatus be calibrated, at the automatic timing means, to compensate for the lag between the production of the pneumatic signal and the actuation of the associated pneumatic valve.
Secondly, because industrial spray coating apparatuses of the type herein described typically provide a selection of between twelve and thirty six alternative colors of paint, a great many pressurized air feed hoses must be provided between the means for sending the pneumatic signal and the pneumatic valves. Spray coating apparatuses of the type herein described are typically manufactured in one location and shipped to the purchaser for assembly by field installers. The field installers must carefully identify and then attach the proper feed hoses at one end to the automatic timing means and at the other end to the pneumatic valves at the color changer. It will be appreciate that this is not only a tedious and time consuming task, but also requires much testing after assembly to ensure the proper placement of the feed hoses.
Additionally, relatively larger diameter feed hoses must be provided between the automatic timing means and the pneumatic valves due to the relatively large distance which must be traversed by the pressurized air. In other words, because of the head loss phenomena, large diameter feed hoses are required to convey sufficient air pressure from the source to the pneumatic valve for actuation. It will be appreciated that a great many large diameter feed hoses extending a significant distance through a spray coating plant substantially increases the costs of the apparatus.